The present invention concerns a conical grinding cutter for use in grinding, or refining, wood pulp, wherein the cutting part constituted by the mantle surface of a cone is assembled of a plurality of separate sectors. A grinder, or refiner, of this type comprises two cone-shaped cutters, the outer and the inner, of which one at least rotates, and their surface facing each other having been provided with an appropriate furrow pattern so that when the cutter is rotating the ridges following each other with a small interval will grind the wood to fine pulp.
In the prior art such conical grinding cutters are known which have been produced by casting in one place. The problem is then, however, that it is difficult to achieve good casting quality; therefore the reject percentage is high, the casting process expensive and the delivery time objectionably long. Causes of foundry technology alone impose major restrictions on the casting of objects of this size and shape, and it is not possible to produce a surface patterning meeting high enough quality standards. Morever, manufacturing of the pattern equipment needed in mold preparation is expensive and time-consuming. In practice, there are furthermore restrictions regarding choice of material.
It is also known to manufacture conical grinding cutters by welding the ridges fast to the mantle one by one. This procedure, too, is expensive and time-consuming, as anybody will realize. Morever, steel ridges of weldable material have no long service life.
Through the Finnish Pat. No. 54,351 is also known a conical grinding cutter assembled of separate steel sectors. By forming the conical grinding cutter of separate cutter sectors one gains the advantage that the casting process is facilitated and rather more fine-feathered cutter patterns can be cast. It is also a remarkable improvement that the casting quality improves and hereby the reject percentage goes down. In addition, the time consumed in preparing the pattern equpiment needed in mold making is short and the work is comparatively inexpensive. However, the drawback is present that the cutter sectors have been interconnected with flanges at their ends only, whereby the construction of the conical grinding cutter is not made rigid enough. We have observed that in the case of cutters requiring such high manufacturing accuracy, where the distance between the cutter surfaces facing each other is only a fractoin of one millimetre, the grinding efficiency is substantially impaired by the least yielding of an inadequately stiffened cutter sector.